PURPOSE: To obtain excellent room heating effect even in cold areas by providing a bypass route in the air route and mounting the heat absorption side heat exchanger of a heat pump as an auxiliary heat source to the bypass route.

CONSTITUTION: On the roof surface which is facing to south an air collector 2 is installed, and an air route 5 which connects both ends of the air collector 2 and a heat storage tank 3 provided under the floor is provided. Further, a heat pump 9 is separately installed and its heat absorption side heat exchanger 9a is provided by the side of the heat storage tank 3, and its heat radiation side heat exchanger 9b is installed at a suitable position in the room. Inside the heat absorption side heat exchanger 9a a bypass route 10 is provided which connects both sides of the heat storage tank 3 by piercing the heat exchanger 9a. Further, an air circulation fan 12 for circulating air through the system 1 is provided on the ceiling of the air route 5a on the side of the route in which the air advances. With this arrangement, room heating with a low running cost can be provided even in cold areas.